NORMAL DIET 585 



BIOLOGICAL VALUES OF VARIOUS PROTEINS, ESTIMATED IN 

 TERMS OF THE PERCENTAGE OF BODY-PROTEIN WHICH 

 THEIR INGESTION WILL SPARE FROM Loss. 



It is evident, therefore, that the nutritive value of peas, for example 

 notwithstanding their remarkably high protein content in comparison 

 with other vegetables is much less than we might infer from their 

 composition, and approximately double the normal protein intake 

 required on a diet in which peas and beans are the only important source 

 of protein. Recollecting that peas and beans are the only generally 

 available vegetable articles of diet in which proteins are at all abundant, 

 the difficulty of securing nitrogenous and calorific equilibrium upon an 

 exclusively vegetable diet must be apparent. The herbivorous animals 

 can accomplish it by eating an enormous bulk of food, for which their 

 intestines are specially adapted by their length and capacity. A pro- 

 portionately bulky diet would insure grave digestive disorders in the 

 average human being to whom it was habitual. 



Even more serious difficulties than this, however, confront the would- 

 be vegetarian. We have seen (Chapter XX) that certain constituents 

 of the diet which are associated solely with Animal Fats are absolutely 

 essential both for maintenance and for growth. These are lacking in a 

 diet composed of customary articles which are solely of vegetable 

 origin. The fat-soluble essentials for growth and maintenance do not 

 occur in the fatty tissues of plants, in seeds and fruits, but in the forage- 

 parts. They are acquired from these by the herbivorous animals and 

 stored by them in their body-fat. To obtain a sufficiency of these 

 substances from vegetables in our diet, we would be compelled to con- 

 sume an excessive quantity of vegetable material of very low nutritive 

 value, containing a very large proportion of indigestible residue. It 

 may therefore be stated, and experience seems to have fully justified 

 this deduction, that continued maintenance of weight and health, and, 

 above all, growth, are impossible of attainment by human beings who 

 confine themselves strictly to a vegetable diet. 



Happily there are few people who are so fanatical in their vegetarian- 

 ism as to attempt to subsist solely upon vegetables, fruits and cereals, 

 and the so-called vegetarian usually partakes fairly freely of Milk and 

 Eggs. On a mixed diet which contains a good proportion of these 

 articles there is no difficulty in securing a thoroughly satisfactory 

 nitrogenous and calorific equilibrium, and experience has demon- 

 strated that a dietary of this character may maintain a high standard 

 of bodily health and vigor. It is not improbable that occasional indi- 



